载脂蛋白E4通过改变钾通道功能导致神经毒作用的机制研究

Apolipoprotein (apo) E4 is a major genetic risk factor for Alzheimer's disease. Emerging biochemical, cell biological, transgenic animal and clinical studies have suggested potential explanations for apoE4's contribution to the pathogenesis of Alzheimer's disease. However, the underlying mechanisms are unclear. .In human brain, apoE is synthesized and secreted primarily by astrocytes, but some neurons produce apoE. Potassium current plays an important role in neurons' excitability and progress of Alzheimer's disease. In our previous study, delayed rectifier potassium channels was observed to be suppressed by intracellular apoE4. In this study, we plan to test the function of potassium currents in the effect on neuron from not only exogenous but also endogenous apoE4, and in the relationship between apoE4 and Alzheimer's disease. First，We will observe the changes of neurons' electrophysiological property and calcium signal by exogenous apoE4. The observation will be carried both on inside and outside of neuron membrane to clarify which side is the major action site. Then, human APOE4 transfected mice neurons will be used to test the effect of endogenous apoE4, including electrophysiological property, calcium signal, Tau phosphorylation, and neuron degeneration et al..Our study about the effect of potassium channels on apoE4's neurotoxicity will find out the prime action site and contribution of apoE4 in Alzheimer's disease, which would be helpful to clinical work on Alzheimer's disease.

载脂蛋白（apolipoprotein , apo）E的ε4等位基因是阿尔茨海默病的主要危险因素，其具体作用机制及初始作用位点尚不清楚。人类大脑apoE主要由星形胶质细胞合成和分泌，神经元自身也能够少量合成；钾电流改变在神经元兴奋性以及阿尔茨海默病中发挥重要作用，并且我们前期工作发现：胞内侧的apoE4能够抑制神经元延迟整流钾通道的活动。本研究的目的在于:从钾通道功能改变的角度关注外源性和内源性apoE4神经毒作用和机制。首先，分别从细胞内和细胞外，研究外源性apoE4对神经元电生理特性和钙信号的影响；在此基础上，诱导神经元自身表达apoE4，考察内源性apoE4对神经元电生理特性、钙信号以及微管相关蛋白Tau的磷酸化、神经元退行性变等的神经毒作用。通过上述研究，揭示钾通道功能改变在apoE4神经毒中的作用及机制，为apoE4相关阿尔茨海默病的临床工作提供理论参考。

载脂蛋白（apolipoprotein , apo）E的ε4等位基因是阿尔茨海默病的主要危险因素。人类大脑神经元自身能够少量合成apoE；钾电流改变在提高神经元兴奋性以及阿尔茨海默病中发挥重要作用。基于上述研究基础，我们从钾通道功能改变的角度，关注外源性和内源性apoE4神经毒作用和机制。我们的工作发现：1）分别从神经元的细胞内和细胞外给予外源性apoE4，神经元膜上的延迟整流钾电流（IK）和快速一过性钾电流（IA）均受到不同程度的抑制，其中，外源性apoE4的抑制作用在神经元内侧的作用更加显著；2）分别从神经元的细胞内和细胞外给予外源性apoE4，神经元的胞内游离钙离子浓度都有所上升，主要来源为胞外钙离子的进入，并可以特异性地被NMDA受体的阻断剂抑制，而钾通道的激动剂可以在一定程度上抑制apoE4的钙超载作用；3）通过装载有人apoE基因的慢病毒感染，诱导小鼠神经元自身表达apoE，我们发现：表达人apoE4的小鼠神经元上，IK和IA的平均电流幅度减小，动作电位的时程延长，放电频率也有所增加。上述现象提示：钾通道活动的抑制可能是apoE4的神经毒作用机制之一；神经元的胞膜内侧可能是apoE4神经毒作用的一个主要位点，而神经元自身表达的apoE4是导致AD患者大脑内神经元功能受损乃至死亡的原因之一。